feat(observability): phase 1 - schema, models & event log backend

Add database foundation for observability features:
- event_log table with severity/source filtering and pagination
- standalone_proxies table for user-created reverse proxies
- stale_threshold_days setting (default 7 days)
- Auto-persist warn/error events from event bus to database
- SSE broadcast of persistent events for real-time UI updates
- Frontend types and API functions for downstream UI phases

plans/observability-proxy-mgmt/phase-6-proxy-creation-ui.md

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+# Phase 6: Direct Proxy Creation UI
+
+**Status:** ⬜ Not Started
+**Parent plan:** [PLAN.md](./PLAN.md)
+**Domain:** frontend
+
+## Objective
+Build the proxy creation form with live validation feedback, diagnostic hints, and management actions (edit/delete).
+
+## Tasks
+
+- [ ] Task 1: Create "Create Proxy" form component — fields: destination URL/IP, port, domain (auto-suggested from subdomain pattern), optional custom subdomain override
+- [ ] Task 2: Live validation — debounced calls to POST /api/proxies/validate as user types (300ms debounce)
+- [ ] Task 3: Validation result display — step-by-step checklist with icons:
+  - ✅ DNS resolution OK / ❌ DNS resolution failed
+  - ✅ TCP port reachable / ❌ TCP port not reachable
+  - ✅ HTTP responding / ❌ HTTP not responding
+  - Each failure shows the diagnostic hint from the backend
+- [ ] Task 4: Create proxy submission — calls POST /api/proxies, shows success toast with health indicator
+- [ ] Task 5: Edit proxy — modal or inline form, pre-populated with current values, re-validates on save
+- [ ] Task 6: Delete proxy — ConfirmDialog with domain name confirmation
+- [ ] Task 7: Integration with proxy viewer page — "Create Proxy" button in the proxy viewer header
+- [ ] Task 8: Domain auto-suggestion — when user enters destination, suggest domain based on subdomain_pattern from settings
+- [ ] Task 9: Add i18n keys for proxy creation
+
+## Files to Modify/Create
+- `web/src/lib/components/ProxyForm.svelte` — NEW: Create/edit proxy form
+- `web/src/lib/components/ValidationChecklist.svelte` — NEW: Step-by-step validation display
+- `web/src/routes/proxies/+page.svelte` — Add "Create Proxy" button and modal/panel
+- `web/src/lib/api.ts` — Ensure validateProxy, createProxy, updateProxy, deleteProxy are present (from Phase 3)
+
+## Acceptance Criteria
+- Form validates destination in real-time with debouncing
+- Each validation step shows pass/fail with diagnostic hints
+- Proxy creation works end-to-end (form → API → NPM → success)
+- Edit and delete work for existing standalone proxies
+- Domain auto-suggestion works from settings pattern
+- Error states handled gracefully (network errors, API failures)
+
+## Notes
+- Validation should show a loading spinner while in progress
+- Don't validate on every keystroke — use 300ms debounce
+- If all validation steps fail, still allow creation (user might know better — just warn)
+- SSL certificate is applied automatically from global settings (no cert picker in form)
+
+## Review Checklist
+- [ ] All tasks completed
+- [ ] Code follows project conventions
+- [ ] No unintended side effects
+- [ ] Build passes
+- [ ] Tests pass (new + existing)
+
+## Handoff to Next Phase
+<!-- Filled in by the implementation agent after completing this phase. -->